The Chihuahua, Pomeranian, Yorkshire terrier and Maltese are American Kennel Club-designated toy dogs. All weigh under 7 pounds. The Yorkshire terrier is the most popular toy breed in the country. It ranks No. 6 on this year's list of breeds.

Small dogs like Yorkies still require big-time care, American Kennel Club spokeswoman Jessica Rice D'Amato said.

"Just because they are small doesn't mean they need less exercise or mental stimulation," she said.

And because the small dogs are so adorable, children tend to squeeze them like they do teddy bears. This can cause injuries, Beilstein said.

Despite the risks and problems of pocket-size pooches, they can give big-time performances.

Pam Shelby, a retired teacher from Beaumont, California, said her Yorkie, Desi, became a champion in agility contests. There's nothing like taking your dog through the hurdling, jumping, climbing and swerving paces of the obstacle-laden contests, she said.